This invention relates to improvements in a wear plate that is specifically designed for convenient and removable installation in the pedestal opening of a railway side frame in order to prevent wear on the load bearing surface of the pedestal. Normally, a bearing adaptor is provided over the axle bearing, said adaptor having a slightly arcuate top surface which bears directly against a corresponding downwardly facing surface in the pedestal opening of the side frame.
In service, limited movement or frictional sliding occurs between the bearing adaptor and the pedestal surface, which may cause worn spots on the frame, resulting in sloppiness and a weakening of the frame at a load bearing location. Repair of the frame surface is both expensive and time consuming, since the worn surface must be ground down and renewed by welding a plate in the opening.
In my U.S. Pat. No. 3,897,736, there is disclosed a renewable wear plate which is removably attached to the side frame in the pedestal opening and constitutes a wear surface against the bearing adaptor. The plate has resilient side lips which resiliently clamp against the sides of the frame and tend to hold the plate in position during installation and service. Means are provided between the frame and the plate to limit longitudinal movement of the plate relative to the frame, in order to minimize wear on the frame.
Although the wear plate described in the aforesaid patent is economical and easy to use, difficulties have arisen because of possible variations in the width of the side frame casting. The wear plate described in U.S. Pat. No. 3,897,736 has a flat bottom wall defining the wear surface, and when clipped onto a side frame having a nominal or less than nominal width (within permitted tolerance range), the wear surface remains flat on the flat surface in the pedestal opening.
Experience has shown that the width of the side frame castings as currently manufactured is almost always greater than the nominal width. For example, if the nominal width at the pedestal roof is 6 inches, the dimension of most side frames will significantly exceed this figure and will typically measure in the order of about 1/16 inches greater than nominal.
The wear plate of the aforesaid patent have opposed lips or flanges extending from the base. The lips are spaced sufficiently, i.e., in the order of 53/4 inches, so that the wear plate may be pressed onto the pedestal roof and the lips will resiliently grip the sides of the pedestal, thereby holding the wear plate in position but still allowing for easy removal.
In connection with the above discussion regarding the spacing between the lips, it is apparent that the spacing must be maintained at a fixed maximum dimension that will insure proper gripping of those occasional side frame castings that have nominal or less than nominal width.
It has been found, however, that the aforesaid wear plate having a flat bottom plate and a fixed maximum dimension between the lips is not ideally suited for side frames having greater than nominal width. Upon installation of the wear plate, the lips are pushed or distended outwardly beyond design limitations. This in turn causes the bottom wall of the plate to bow in a concave fashion, thereby creating an excessive gap between the pedestal roof and the wear plate near the edges. This in turn causes a dramatic increase in the stress in the plate when the gap is forced to close due to movement of the side frame and axle bearing adaptor toward each other.
As a result of the foregoing situation, the nominal stress level on the wear plate may be doubled. This higher stress, coupled with a wide stress range, as cycling takes place, can result in early fatigue failure of the lip or flange, and complete loss of the gripping force.